Efficient Removal of Volatile Organic Compounds by FAU-Type Zeolite Coatings.

Silicone and pure organic binders were used to develop FAU-type zeolite coatings applied on pre-treated aluminum substrates by using a spraying method and then cured under specific conditions. The influence of the amount of binder on adhesion properties of zeolite coatings was first investigated to determine the optimum ratio between zeolite and binder. Zeolite coatings were then elaborated with a high zeolite content (between 70 and 80 wt.%) to ensure high adsorption capacities. The amount of binders involved in different zeolite coatings was sufficient to achieve interesting adhesion and cohesion properties. The accessibility of zeolite microporosity was studied by nitrogen adsorption-desorption measurements, which revealed a very small or no loss of the micropore volume for the optimized coatings. Volatile Organic Compounds (VOCs) adsorption measurements were carried out using n-hexane as probe molecule. FAU-type zeolite in powder form adsorbs 180 mg/ganhydrous zeolite, whereas the amounts of n-hexane adsorbed by zeolite coatings ranged from 131 to 175 mg/ganhydrous zeolite.

Modeling SOx trapping on a copper-doped CuO/SBA-15 sorbent material.

A mixture of SO2 and air was continuously injected in a fixed bed reactor containing a CuO/SBA-15 sorbent material and submitted to an isothermal temperature between 325 and 400 °C. The SO2 emissions were measured at the exit of the reactor. Different isothermal temperatures, different injected SO2 concentrations and different sorbent masses, all representative of industrial conditions, were tested. The purpose of the paper was to propose efficient global models which simulate the breakthrough curves whatever the experimental conditions. A simplified model was first considered assuming that the oxidation and trapping processes can occur on each copper site. The values of the four kinetic parameters which are involved were determined solving this model using Scilab software and an optimization routine. Because this model failed to reproduce in a satisfying way the breakthrough curves for different sorbent masses, a second model was introduced which involves surface and bulk trapping sites and six kinetic parameters. The breakthrough curves simulated with this second model following the same resolution techniques were in better agreement with the experimental ones, whatever the experimental conditions. For comparison, a simulation of the breakthrough curves returned by a model with bulk diffusion was presented.

New functionalized MIL-53(In) solids: syntheses, characterization, sorption, and structural flexibility.

The syntheses and characterization of a series of functionalized MIL-53(In) solids have been reported. Chemical groups with variations in steric hindrance and chemical nature (-(OH)2, -Br or -NO2 groups) were introduced through the terephthalate linker to modify the pore surface. Single crystal X-ray diffraction data, N2 adsorption-desorption isotherms, and infrared spectra were systematically investigated to explore the impact of the functional groups grafted onto the organic linker on the dynamic behaviour of these highly flexible hybrid porous frameworks. Owing to the distinctive steric hindrance and chemical nature, the different substituents can influence the interactions between the framework and the trapped molecules, further influencing the flexibility of the materials. Dihydroxyl modified MIL-53(In) exhibits no nitrogen accessible porosity. Notably, functionalization by -Br and -NO2 groups leads to the different capabilities of the corresponding solids to accommodate N2 molecules.

Adsorption of 1,2-dichlorobenzene and 1,2,4-trichlorobenzene in nano- and microsized crystals of MIL-101(Cr): static and dynamic gravimetric studies.

This work aims to highlight the promising adsorption capacity and kinetic of (poly)chlorobenzene pollutants in the hybrid MIL-101(Cr) type material for technological uses in industrial waste exhaust decontamination. The influence of the MIL-101(Cr) crystal size (nano- and microcrystals) on the adsorption behavior was studied in static and dynamic modes. For this purpose, crystals of MIL-101(Cr) in nano- and micrometric sizes were synthesized and fully characterized. Their sorption properties regarding 1,2-dichlorobenzene were examined using gravimetric method in dynamic (p/p° = 0.5) and static (p/p° = 1) modes at room temperature. 1,2,4-trichlorobenzene adsorption was only performed under static mode because of its too low vapor pressure. 1,2-dichlorobenzene and 1,2,4-trichlorobenzene were used to mimic 2,3-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin, respectively, and more largely dioxin compounds. Adsorptions of these probes were successfully carried out in nano- and microcrystals of MIL-101(Cr). Indeed, in static mode (p/p° = 1) and at room temperature, nanocrystals adsorb 2266 molecules of 1,2-dichlorobenzene and 2093 molecules of 1,2,4-trichlorobenzene per unit cell, whereas microcrystals adsorb 1871 molecules of 1,2-dichlorobenzene and 1631 molecules of 1,2,4-trichlorobenzene per unit cell. In dynamic mode, the 1,2-dichlorobenzene adsorbed amounts are substantially similar to those obtained in static mode. However, the adsorption kinetics are different because of a different scheme of diffusivity of the adsorbate between the two modes. To the best of our knowledge, these adsorption capacities of MIL-101(Cr) as adsorbent for polychlorobenzenes trapping have never been referenced. MIL-101(Cr) appears as a promising material for technological uses in industrial waste exhaust decontamination.

Intrusion-extrusion spring performance of -COK-14 zeolite enhanced by structural changes.

-COK-14 zeolite, the variant of COK-14 (OKO topology) with a systematically interrupted framework, exhibits unusual behaviour in high pressure intrusion-extrusion cycles of 20 M LiCl solution. After the first cycle with deviating behaviour and partially irreversible intrusion, subsequent cycles show stable reversible behaviour. The system behaves like a spring with unique progressive intrusion in the range of 10-120 MPa followed by enhanced uptake before saturation. While the intrusion-extrusion cycling leads to fragmented crystals, powder diffraction reveals high crystallinity of the fragments. Based on the detailed characterisation of the zeolite samples with XRD, Rietveld refinement, N2 adsorption, TGA and (29)Si MAS NMR before and after intrusion-extrusion experiments, a model of the structure of the intruded -COK-14 samples is proposed. Intrusion-extrusion of LiCl solution systematically breaks the most strained bonds in the structure which results in a new framework connectivity with enhanced stability, which persists during the harsh intrusion-extrusion conditions.

Assessment of the energetic performances of various ZIFs with SOD or RHO topology using high pressure water intrusion-extrusion experiments.

The energetic performances of seven SOD or RHO-topology ZIFs, with zinc or cobalt metal cation (ZIF-8, ZIF-90, Zn(dcim)2-SALE, ZIF-67, ZIF-7, ZIF-71, ZIF-11) were evaluated using water intrusion-extrusion under high pressure. The relationship between the structural parameters (in particular the pore system SOD or RHO, the type of linker, the metal cation nature) and the intrusion pressure was studied to better understand the mechanism of water intrusion and the energetic behaviour for a given ZIF crystal type. "ZIF-8-water", "ZIF-67-water" and "ZIF-71-water" systems display a shock-absorber behaviour. A very important hysteresis for ZIF-71 and a slight difference between the first intrusion-extrusion cycle and the following ones for ZIF-67 were observed. ZIF-8 (SOD) with zinc cation and ZIF-67 (SOD) with cobalt cation display similar intrusion pressures. For ZIF-71 (RHO) material, the stored energy is more than doubled compared to ZIF-8 and ZIF-67 (SOD). This might be related to the topology. No water intrusion was observed after three water intrusion-extrusion cycles, for the ZIF-90 (SOD), Zn(dcim)2-SALE (SOD), ZIF-7 (SOD) and ZIF-11 (RHO) materials. This is explained in term of hydrophilic feature as well as topology and linker effects.

Prediction of the mechanical properties of zeolite pellets for aerospace molecular decontamination applications.

Zeolite pellets containing 5 wt % of binder (methylcellulose or sodium metasilicate) were formed with a hydraulic press. This paper describes a mathematical model to predict the mechanical properties (uniaxial and diametric compression) of these pellets for arbitrary dimensions (height and diameter) using a design of experiments (DOE) methodology. A second-degree polynomial equation including interactions was used to approximate the experimental results. This leads to an empirical model for the estimation of the mechanical properties of zeolite pellets with 5 wt % of binder. The model was verified by additional experimental tests including pellets of different dimensions created with different applied pressures. The optimum dimensions were found to be a diameter of 10-23 mm, a height of 1-3.5 mm and an applied pressure higher than 200 MPa. These pellets are promising for technological uses in molecular decontamination for aerospace-based applications.

Ammonium and potassium removal from swine liquid manure using clinoptilolite, chabazite and faujasite zeolites.

This study concerns cationic exchanges performed in order to remove ammonium and potassium cations from manure by using various zeolites: clinoptilolite, chabazite and NaX faujasite. First, the effect of temperature (25 °C and 40 °C) on the exchange rate between zeolites and an ammonium chloride solution was investigated. Then, cationic exchanges were performed on these three zeolites using on one side a mixed ammonium and potassium chloride solution reproducing the chemical composition of a swine manure and on the other side the corresponding liquid manure. No significant difference was observed on the exchange rate and the trapping of ammonium cations by changing the temperature (25 or 40 °C). Clinoptilolite showed a good selectivity towards ammonium cations using model (NH4Cl, and mixed NH4Cl/KCl) solutions but is less efficient with the liquid manure. Chabazite and faujasite were found more efficient than clinoptilolite for trapping ammonium cations. However, NaX faujasite enables trapping 3 times more ammonium cations than chabazite from manure (60 and 20 mg/g, respectively). Moreover, chabazite allowed to trap the same amount of potassium cations than NaX faujasite (33 and 35 mg/g, respectively).

Energetic behavior of the pure silica ITQ-12 (ITW) zeolite under high pressure water intrusion.

Experimental water intrusion-extrusion isotherms were obtained at room temperature on pure silica ITW-type zeolites (ITQ-12 zeosil). The water intrusion is obtained by applying a high hydraulic pressure corresponding to the intrusion step. When the pressure is released, the water extrusion occurs at a similar pressure to that of the intrusion one. Therefore, the "ITW zeosil-water" system behaves like a spring and the phenomenon is reproducible over several cycles. Several characterization techniques have been performed before and after water intrusion-extrusion experiments in order to reveal the presence or the lack of defects after such experiments. Structural modifications at the long range order cannot be observed by XRD analysis after three water intrusion-extrusion cycles. However, solid state NMR spectroscopy provides evidence of the presence of Q3 groups revealing the breaking of some siloxane bridges after the intrusion step. The "ITW zeosil-water" system can restore 100% of the stored energy corresponding to about 8 J g(-1).

Energetic performances of the metal-organic framework ZIF-8 obtained using high pressure water intrusion-extrusion experiments.

The "ZIF-8-water" system displays reproducible shock-absorber behaviour over several cycles with a stored energy of 13.3 J g(-1) and an energy yield close to 85%. The combination of the main features evidenced for ZIF-8, i.e. a quite low intrusion pressure and a high stored energy, opens a field for new applications.

Core-shell H-ZSM-5/silicalite-1 composites: Brønsted acidity and catalyst deactivation at the individual particle level.

A combination of in situ UV-Vis and confocal fluorescence micro-spectroscopy is applied to investigate the influence of an external silicalite-1 shell on the Brønsted acidity and coke formation process of individual H-ZSM-5 zeolite crystals. Three probe reactions were used: oligomerization of styrene, methanol-to-olefin (MTO) conversion and aromatization of light naphtha (LNA) derivatives. Oligomerization of styrene leads to the formation of optically active carbocationic oligomers. Different styrene substitutions indicate the conversion ability of the catalyst acid core, a preferred alignment of the oligomers within the straight zeolite channels and a Brønsted acidity gradient throughout the zeolite crystal. Both the MTO conversion and the LNA process lead to limited carbonaceous deposition within the external silicalite-1 layer. This outer shell furthermore prevents the growth of extended coke species at the zeolite external surface. During MTO, the formation of carbonaceous compounds initiates at the center of the H-ZSM-5 zeolite core and expands towards the zeolite exterior. This coke build-up starts with a 420 nm UV-Vis absorption band, assigned to methyl-substituted aromatic carbocations, and a second band around 550 nm, which is indicative of their growth towards larger conjugated systems. Aromatization of linear and branched C5 paraffins causes negligible darkening of the zeolite crystals though it forms fluorescent coke deposits and their precursors within the H-ZSM-5 catalyst. Olefin homologues on the contrary cause pronounced darkening of the zeolite composite. Methyl-branching of these reactants slows down the coke formation rate and produces carbonaceous species that are more restricted in their molecular size.

Surfactant-modified MFI nanosheets: a high capacity anion-exchanger.

Surfactant-Modified MFI-Zeolite Nanosheets (SMZN) were used for the first time as anion-exchangers, in the case of nitrate ion removal. The SMZN material is characterized by high anionic exchange capacity and removal efficiency compared to classical SMZ prepared from clinoptilolite. The SMZN material is easily regenerated and could be probably employed to remove other anionic pollutants.

New insights in the formation of silanol defects in silicalite-1 by water intrusion under high pressure.

The "water-silicalite-1" system is known to act as a molecular spring. The successive intrusion-extrusion cycles of liquid water in small crystallites (6 × 3 × 0.5 µm(3)) of hydrophobic silicalite-1 were studied by volumetric and calorimetric techniques. The experiments displayed a decrease of the intrusion pressure between the first intrusion-extrusion cycle and the consecutive ones, whereas the extrusion pressures remained unchanged. However, neither XRD studies nor SEM observations revealed any structural and morphological modifications of silicalite-1 at the long-range order. Such a shift in the value of the intrusion pressure after the first water intrusion-extrusion cycle is attributed to the creation of silanol groups during the first water intrusion. Detailed FTIR and solid-state NMR spectroscopic characterizations provided a molecular evidence of chemical modification of zeolite framework with the formation of local silanol defects created by the breaking of siloxane bonds.

IM-19: a new flexible microporous gallium based-MOF framework with pressure- and temperature-dependent openings.

Five metal-organic frameworks (MOFs) based on the same three-dimensional gallium terephthalate network (IM-19) are described, and an incommensurate structure (for the as-synthesized form) as well as two remarkable guest-free polymorphs (open and closed) are highlighted.

Thermodynamics of water intrusion in nanoporous hydrophobic solids.

We report a joint experimental and molecular simulation study of water intrusion in silicalite-1 and ferrerite zeolites. The main conclusion of this study is that water condensation takes place through a genuine first-order phase transition, provided that the interconnected pores structure is 3-dimensional. In the extreme confinement situation (ferrierite zeolite), condensation takes place through a continuous transition, which is explained by a shift of both the first-order transition line and the critical point with increasing confinement. The present findings are at odds with the common belief that conventional phase transitions cannot take place in microporous solids such as zeolites. The most important features of the intrusion/extrusion process can be understood in terms of equilibrium thermodynamics considerations. We believe that these findings are very general for hydrophobic solids, i.e. for both nonwetting as well as wetting water-solid interface systems.

Pure silica chabazite molecular spring: a structural study on water intrusion-extrusion processes.

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays real spring behavior. However, differences in pressure-volume diagrams are observed between the first and the other intrusion-extrusion cycles, indicating that some water molecules interact with the inorganic framework after the first intrusion. (29)Si and especially (1)H solid-state NMR showed the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the supercage of Si-CHA: a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules undergoing interaction with the first layer. This hydrogen bonding scheme is also supported by X-ray powder diffraction.

First zeolite carbon replica with a well resolved X-ray diffraction pattern.

The present study demonstrates that for the nanocasting process with zeolites, a careful choice of the zeolite structure type (EMT) allows the formation of faithful carbon replica exhibiting up to three well resolved XRD peaks.

Fluorescence probing investigation of the mechanism of formation of MSU-type mesoporous silica prepared in fluoride medium.

The mechanism of formation of a MSU-type siliceous material from tetraethyl orthosilicate (TEOS) in the presence of the nonionic surfactant tergitol T-15-S-12, sulfuric acid, and sodium fluoride has been investigated using mainly fluorescence probing techniques and, to a lesser extent, dynamic light scattering (DLS) and 29Si NMR spectroscopy. The tergitol micelles present in the systems obtained by progressively generating the reaction mixture giving rise to the mesostructured material by adding to an appropriate tergitol solution sulfuric acid, TEOS, and NaF were characterized by fluorescence probing (micelle aggregation number, micropolarity, and microviscosity) and also by dynamic light scattering (apparent micelle diameter). 29Si NMR experiments were also performed on selected systems after hydrolysis of the TEOS. The fluorescence probing techniques were also used to follow the changes of micelle characteristics with time during the evolution of the full reaction mixture from a limpid solution to a system containing a minor amount of condensed siliceous material. The synthesized solid material was characterized by X-ray diffraction and nitrogen adsorption-desorption analyses. The micelle aggregation number N was found to change only little, and the micropolarity remained constant when going from the tergitol solution to the full reaction mixture. The results of DLS measurements agree with this finding. Besides, while the condensation of silica took place after addition of NaF, the N value increased only very little with time up to the point where a small amount of mesostructured material precipitated out. These results indicate that the interaction between tergitol micelles and the siliceous species formed in the system by the hydrolysis of TEOS and also between micelles and the growing siliceous species must be very weak. As in our previous studies of the mechanism of formation of MCM41-type material from sodium silicate in the presence of cetyltrimethylammonium bromide, it appears that the locus of formation of the mesostructured material is not the micelle surface but the bulk phase. Micelles only act as reservoirs of surfactant providing surfactant monomer that binds to the growing siliceous species.

Carbon and SiC macroscopic beads from ion-exchange resin templates.

A method for preparing carbon and SiC macroscopic beads using ion-exchange resins as a macrotemplate that determines the macroshape and the pore structure of the product materials is reported. First, silicates are ion-exchanged into the resins to prevent the resin from collapsing during subsequent carbonization and allow them to be used as precursors for SiC formation. SiC is prepared via carbothermal reduction of carbon/silica composite beads obtained upon carbonization of the resin/silicate in an inert atmosphere. Finally, silica is removed by HF etching. Very high-surface area (1670-2026 m2 g-1) micro- or micro-/mesoporous carbon beads and relatively high-surface area (35-63 m2 g-1) macro- and meso-/macroporous SiC beads were prepared by the described method. The pore structure and the macroshape of the particles were controlled by the type of ion-exchange resins employed, gel or macroreticular.